The present invention generally relates to high speed cable or wire stranders, and more specifically to a high speed rigid-type cage strander in which the axes of the bobbins are oriented at angles substantially normal to the axis of rotation of the strander and wire take-off takes place without bobbin rotation.
When manufacturing a cable from a plurality of wires, a core wire formed by either a single wire or a plurality of already stranded wires is usually passed through the machine and other wires are wrapped around the core wire either while the core wires move along its path or at the end of the machine. This function is usually carried out by high speed machines which, as a rule, include one or more rotatable frames or housings and a plurality of wire-carrying bobbins located within the frame or carried by supports mounted on the frames.
The core wire is usually paid-off from a bobbin mounted outside the frame and passed through the frame through a path either along the axis of rotation of the frame or displaced from the axis of rotation of the frame. The way the core wire is handled characterizes the type of wire strander and its application.
If the core wire is passed through the machine along its axis of rotation, the wire carrying bobbins rotate around it and the wires paid-off are wound on the core wire at several points along the machine. This system allows the manufacture of conductors with a high number of wires and a change in direction of the various layers since the machine is composed of many cage sections independent of each other. Futhermore, since the core wire passes substantially along the axis of the machine, a large multi-stranded core can be used.
If the core wire is passed through the machine along a path significantly displaced from the axis of rotation of the frame, the wire carrying bobbins are positioned inside the frame along its axis of rotation and they remain stationary while the frame rotates. The cable wires are paid-off from the bobbins and the wires pass through a path displaced from the axis of rotation of the machine and are wound around the core wire at the end of the machine. This method allows the manufacture of conductors with a relatively low number of wires and the various layers of the stranded conductors must be wound in the same direction.
In the past, wire carrying bobbins mounted on the frame of the strander have usually been mounted so that the bobbins were required to rotate along their longitudinal axis in order to pay-off the wire. This arrangement usually requires some control of the rotation of the bobbins, such as a brake mechanism for each bobbin to provide the required wire tension and to assure that the bobbins will not continue to rotate when the frame of the strander has stopped its rotation.
The braking device causes the tension of the wire paid-off from the bobbins to vary during the operation of the strander since the wire pulling tension required to make the bobbin rotate is different when the bobbin is full or near empty. If the initial braking force is adjusted for a full bobbin, the same braking force applied to a bobbin with partially depleted wire supply is sometimes sufficient to cause unacceptable stretch, especially for wires of the smaller gauge. In such a case, the cable produced will be malformed. Also, since the braking force is applied to each bobbin before the initial start of the strander, there is a tendency to stretch the wire before the strander reaches its normal operational speed. Because of frequent malfunction of the brakes, the wires from the bobbins within the frame of the strander occasionally continue to pay-out after the strander has been stopped, and because different brake forces are applied to different bobbins, different tensions are created in the wire paid-out from the bobbins. Therefore, many times the cable formed by traditional stranders have one or more wires loosely wrapped with the remaining wire more tightly wrapped.
Most known stranders being used in the manufacture of stranded cable from a plurality of wires have additional disadvantages. Unloading of empty bobbins and loading of full bobbins is normally a time consuming process and can result in a substantial down time of the machine. In some instances, bobbins must be handled individually during loading and unloading. At best, the prior art teaches the simultaneous loading and unloading of a single row of bobbins. For example, for a twenty-four bobbin rotor, it may take almost one half an hour to load and unload even with the most advanced machines.
Safety has always been a concern with respect to stranding machines since they normally rotate at high speeds and carry very heavy bobbins. Failure of a machine which causes accidental release of a bobbin during operation can result in substantial personal injury and property damage. While numerous approaches have been proposed to minimize such accidents, many machines are still not sufficiently safe.